Method for processing a gaseous composition

ABSTRACT

A process can treat a gaseous material mixture obtained by catalytic conversion of synthesis gas that contains at least alkenes, possibly alcohols and possibly alkanes, and also possibly nitrogen as inert gas and unconverted components of the synthesis gas, comprising hydrogen, carbon monoxide and/or carbon dioxide. After catalytic conversion of synthesis gas, separation of the product mixture obtained in this reaction into a gas phase and a liquid phase is performed by at least partial absorption of the alkenes, possibly of the alcohols and possibly of the alkanes, in a high boiling point hydrocarbon or hydrocarbon mixture as an absorption medium, separation as the gas phase of the gases not absorbed into the absorption medium, separating an aqueous phase from the organic phase of the absorption medium, preferably by decanting, and desorption of the alkenes, possibly of the alcohols and possibly of the alkanes, from the absorption medium.

The present invention relates to a process for the treatment of agaseous material mixture which has been obtained by catalytic conversionof synthesis gas, this material mixture containing at least alkenes,possibly alcohols and possibly alkanes, and also possibly nitrogen asinert gas and unconverted components of synthesis gas, comprisinghydrogen, carbon monoxide and/or carbon dioxide, in which, after thecatalytic conversion of the synthesis gas, at least one stage isprovided in which a separation of the product mixture obtained in thisreaction into a gas phase and a liquid phase is carried out.

Recovery of Synthesis Gas from Smelter Gases

WO 2015/086154 A1 describes a process for the operation of an integratedplant for steel production, in which such an integrated plant comprises,inter alia, a blast furnace for pig iron production and a convertersteel works for crude steel production. In the blast furnace process,CO, CO₂, hydrogen and steam are produced as products of the reductionreactions, the blast furnace waste gas drawn off from the blast furnaceprocess exhibiting, in addition to the abovementioned constituents,still a high content of nitrogen. A blast furnace waste gas comprises,for example, from 35% to 60% by volume of nitrogen, from 20% to 30% byvolume of carbon monoxide, from 20% to 30% by volume of carbon dioxideand from 2% to 15% by volume of hydrogen.

In a converter steel works, which is arranged downstream of the blastfurnace process, pig iron is converted into crude steel. By blowingoxygen onto liquid pig iron, troublesome impurities, such as carbon,silicon, sulfur and phosphorus, are removed. A converter gas whichexhibits a high content of carbon monoxide and also comprises nitrogen,hydrogen and carbon dioxide is drawn off from the steel converter. Atypical converter gas composition exhibits from 50% to 70% by volume ofcarbon monoxide, from 10% to 20% by volume of nitrogen, approximately15% by volume of carbon dioxide and approximately 2% by volume ofhydrogen.

A coking plant can furthermore be operated in such an integrated plant,in which coal is converted into coke by a coking process. In the cokingof coal to give coke, a coke oven gas is obtained, which gas comprises ahigh hydrogen content and considerable amounts of methane. Typically,coke oven gas comprises from 55% to 70% by volume of hydrogen, from 20%to 30% by volume of methane, from 5% to 10% by volume of nitrogen andfrom 5% to 10% by volume of carbon monoxide.

WO 2015/086154 A1 describes the possibility of using blast furnace wastegas, converter gas and coke oven gas, which are also described in theirtotality as smelter gas, for the production of chemical compounds, itbeing possible for the crude gases, individually or in combination as amixed gas, to be recovered and then to be supplied as synthesis gas to achemical plant. In concrete terms, methanol or generally andnonspecifically “other hydrocarbon compounds” are mentioned as possiblechemical compounds which can be produced from such a synthesis gasobtained from smelter gases. Furthermore, a biochemical use of thesynthesis gas for the production of ethanol or butanol via afermentation is mentioned. However, the production of higher alcoholsfrom the synthesis gas is not treated in more detail in thispublication.

In the treatment of these crude gases, a gas purification is generallycarried out for the separation of troublesome ingredients, in particulartar, sulfur, sulfur compounds, aromatic hydrocarbons and high boilingpoint aliphatic hydrocarbons. In addition, a gas conditioning is for themost part carried out, in which the proportion of the components carbonmonoxide, carbon dioxide and hydrogen within the crude gas is changed.The plan of the use described above of smelter gases for the productionof chemical products is also denoted as Carbon2Chem® process.

State of the Art Concerning the Production of Alcohols and Alkenes byCatalytic Conversion of Synthesis Gas

EP 0 021 241 B1 discloses a process for the production of mixtures ofacetic acid, acetaldehyde, ethanol and alkenes with two to four carbonatoms by conversion of synthesis gas comprising carbon monoxide andhydrogen in the gas phase over supported catalysts, the catalystscomprising rhodium and from 0.1% to 5.0% by weight of sodium orpotassium. The oxygen-containing compounds and the alkenes are formed ina molar ratio of 1:1 to 2.5:1. The selectivity for the alcohols of thecatalysts used is comparatively poor. Conversion at a pressure of 20bar, a temperature of 275° C. and a ratio of carbon monoxide to hydrogenin the synthesis gas of 1:1 produces more than 20% of acetic acid,approximately 12-20% of acetaldehyde, about 5% to 10% of ethene, acomparatively high proportion of propene of sometimes more than 20%,varyingly large proportions of methane and only a few percent ofethanol, about 2.5% to 7%. This known process seeks to produce mixturesof oxygen-containing C2 compounds and a high proportion of low molecularweight alkenes and to reduce the proportion of methane. Processes forthe separation of the families from the mixture obtained are notdescribed

U.S. Pat. No. 6,982,355 B2 describes an integrated Fischer-Tropschsynthesis for the production of linear and branched alcohols andalkenes, in which initially a light fraction and a heavy fraction areseparated from one another, the light fraction is brought into contactwith a dehydration catalyst in order to obtain a light fractioncomprising alkenes and alkanes which is then further divided intofractions comprising C5-C9 and C10-C13 alkenes and alkanes, which arethen reacted with synthesis gas partly to give the aldehydes with thecorresponding chain lengths. The aldehydes present in the alkanefraction are subsequently reacted with hydrogen to produce thecorresponding alcohols which remain in the alkane fraction. In a firstdistillation these alcohols are separated from the alkanes and, in afurther distillation, the individual alcohols are obtained from theC5-C9 fraction and the C10-C13 fraction. The alkanes of thecorresponding fractions can be dehydrogenated to give the alkenes. Useis made, as catalysts in the Fischer-Tropsch synthesis, of cobalt, iron,ruthenium or other group VIIIb transition metals, optionally on an oxidesupport, such as silicon dioxide, aluminum oxide or titanium oxide.

CN108067235A describes catalysts for the production of alkenes fromsynthesis gas which comprise cobalt and cobalt carbide as activecomponent, lithium as additive and one or more further metals selectedfrom manganese, zinc, chromium and gallium. Besides the alkenes, thereaction also produces higher alcohols. When using these catalysts, theselectivity for an alkene mixture is said to be up to 40% and that for amixture of alcohols at 30%. Straight-chain alkenes with 2 to 30 carbonatoms and primary alcohols with corresponding chain lengths areobtained. The product mixture comprises predominantly alkanes andalkenes and, depending on the catalyst, about 20% to 25% of alcohols,both methanol, alcohols with 2 to 5 carbon atoms as well as higheralcohols with 6 or more carbon atoms being produced, the latter group ofalcohols forming the predominant proportion and usually being formed tomore than 50%. The publication does not elaborate on the separation ofthe various products present in the mixture.

CN108014816A describes catalysts for the reaction of carbon monoxidewith hydrogen for the production of mixed primary alcohols and alkenes.Use is made of catalysts based on cobalt, in particular dicobaltcarbide, and manganese, on an activated carbon support which cancomprise additions of cerium, copper, zinc or lanthanum. Primaryalcohols and alkenes with 2 to 30 carbon atoms are formed. The catalystsused here are said to have a high selectivity for alkenes, it beingmentioned that alkenes produced can be further converted to alcohols byhydroformylation. Depending on the type of catalyst used, the catalyticconversion of the synthesis gas produces about 23% to 28% by weight ofalkanes, about 36% to 41% by weight of alkenes and about 20% to 21% byweight of higher alcohols, at the same time about 8% by weight ofmethane and about 2% to 5% by weight of carbon dioxide and about 1% to2% by weight of methanol being produced.

U.S. Pat. No. 8,129,436 B2 describes a process for the production of analcohol mixture from synthesis gas, a mixture of alcohols andoxygen-containing compounds being obtained. It is proposed to strip theproduct mixture with a methanol-containing stream in order to remove aproportion of the carbon dioxide as well as inert gases present in theproduct stream. It is also possible to carry out a downstreamdehydration in order to convert a portion of the ethanol and alsopossibly propanol produced into the corresponding alkenes.Potassium-modified molybdenum sulfide catalysts are used in theconversion of the synthesis gas. This known process gives very complexproduct mixtures which do not comprise alkenes but do compriserelatively small amounts of alkanes, besides C2-C5 alcohols, sometimesrelatively high proportions of methanol and many other oxygen-containingcompounds, such as aldehydes, carboxylic acids, ketones, esters orethers, and also mercaptans and alkyl sulfides.

US 2010/0005709 A1 describes alternative fuel compositions comprisingethanol, isopropanol and butanols, in which synthesis gas is initiallyconverted by a Fischer-Tropsch synthesis into a C2-C4 alkene stream andsubsequently these alkenes are hydrated. The alcohols obtained can beblended with gasoline in order to obtain fuel compositions. Theconversion of synthesis gas described in this document gives only about39% of hydrocarbons with 2 to 4 carbon atoms while about 40% of higherhydrocarbons, cycloalkanes and aromatic C5 to C20 compounds, such as aretypically present in gasoline or diesel, are formed. This hydration ofthe C2-C4 alkenes can only give a maximum of 39% of alcohols, which,besides ethanol, are secondary alcohols and also tertiary butanol.Methanol, 1-propanol and 1-butanol are not formed. This known processemploys, in a variant of the Fischer-Tropsch synthesis, iron-manganesecatalysts with contents of zinc oxide and potassium oxide. This reactionproduces almost exclusively C2-C4 alkenes and 9.6% of methane and 15.7%of C2-C4 alkanes while primarily not forming any alcohols, so that thealcohols are only acquired in a further stage through hydration of thealkenes. Since the product mixture is subsequently mixed with gasolineto give a fuel, it is not absolutely necessary to separate the alkanesor the compounds with 5 carbon atoms or longer carbon chains.

U.S. Pat. No. 5,237,104 A describes a process for the hydroformylationof a hydrocarbon-containing feed stream using a cobalt-containingcatalyst. The aim of the hydroformylation is the production of higheralcohols and aldehydes by chain lengthening, in which here thehydrocarbon-containing feed stream is reacted with a synthesis gas. Thisknown process is concerned, in the course of the treatment of theproduct mixture, with separating the cobalt compounds from the mixture.For this, the volatile cobalt compounds are brought into contact with anolefinic absorbent which exhibits a relatively high molecular weight andcomprises, for example, a chain with 10 to 14 carbon atoms.

U.S. Pat. No. 4,510,267 A describes a process for the production ofalkenes from synthesis gas in which ruthenium catalysts on a ceriumoxide support are used. It is described that the catalyst is selectivefor the production of alkenes with a low proportion of methane. In orderto keep the yield of methane low, a low molar ratio of hydrogen tocarbon monoxide in the synthesis gas is recommended. Besides methane,C2-C6 alkenes and, in relatively low amounts, C2-C6 alkanes areproduced. Separating processes for the separation of the product mixtureare not described in this document. Alcohols (methanol and ethanol) areonly formed in very low amounts.

US 2014/0142206 A1 describes a process for the production of a catalystcomprising cobalt and molybdenum on a carbon support. The catalyst isused for the production of alcohols from synthesis gas, in which a highyield of C2 and C3 alcohols is described. The conversion is carried outunder the conditions of a Fischer-Tropsch synthesis. Separatingprocesses for the recovery of individual product groups or individualcompounds from the product mixture obtained after the conversion are notdescribed in this document.

GENERAL DESCRIPTION OF THE PRESENT INVENTION

In the abovementioned Carbon2Chem® process, smelter gases are used andtreated such that a synthesis gas is produced which is suitable inprinciple for the production of chemical compounds. This synthesis gascan be converted in a catalytic synthesis to give higher alcohols.Because of the different composition of the synthesis gas and thedifferences in the conditions of the subsequent conversion of thesynthesis gas, the product mixture obtained in the process described inthe present patent application differs from that of a conventionalFischer-Tropsch synthesis, which starts out from natural gas.

After the catalytic synthesis of higher alcohols by conversion of asynthesis gas recovered from smelter gases, a gaseous mixture isobtained which comprises hydrogen, carbon monoxide, nitrogen, carbondioxide, methane and water as well as various alkanes, in particularethane, propane, butane, pentane, the corresponding alkenes, inparticular ethylene, propylene, 1-butylene, 1-pentylene, and alcohols,in particular methanol, ethanol, 1-propanol, 1-butanol and also possibleisomers of these alcohols, in particular 2-propanol, isobutanol,tert-butanol, 2-butanol, the latter not being explicitly looked at inmore detail here since their behavior corresponds essentially to that of1-propanol or 1-butanol. Only a few percent of the gaseous productstream are useful materials, in particular the alcohols and the alkenes.For example, up to 90% or more are, on the other hand, light gases whichnoticeably impede the condensation of the product mixture.

The object of the present invention consists in making available animproved process for the treatment of a gaseous material mixture whichhas been obtained by catalytic conversion of synthesis gas, in which thelight gases are largely separated and then the product mixture is sotreated further that the useful materials present in this, in particularthe alcohols and alkenes, can be recovered as completely as possible.

The abovementioned object is achieved by a process for the treatment ofa gaseous material mixture of the type mentioned at the outset with thecharacteristics of claim 1.

The treatment of the gaseous material mixture comprises, according tothe invention, at least the following stages:

-   -   separation of the product mixture into a gas phase and a liquid        phase by at least partial absorption of the alkenes, possibly of        the alcohols and possibly of the alkanes, in a high boiling        point hydrocarbon or hydrocarbon mixture as absorption medium;    -   separation as gas phase of the gases not absorbed into the        absorption medium;    -   separation of an aqueous phase from the organic phase of the        absorption medium, preferably by decanting;    -   desorption of the alkenes, possibly of the alcohols and possibly        of the alkanes from the absorption medium.

If, in the context of the present invention, a synthesis gas recoveredfrom smelter gases might be used, it is possible, for example, toproceed as follows. Blast furnace waste gas and converter gas areoptionally purified, for example in order to remove solids and/orcatalyst poisons present in these gases. If coke oven gas is also used,then the purification thereof is for example advantageously by apressure swing adsorption (PSA), so that predominantly hydrogen isrecovered from the coke oven gas. The proportion of hydrogen of thesynthesis gas can optionally be increased, by adding hydrogen producedby electrolysis using electricity from renewable energy sources. Thecarbon dioxide content of the synthesis gas can optionally be reduced bya reverse water gas shift reaction, in which the carbon dioxide isconverted into carbon monoxide. The treated synthesis gas obtained inthis way from smelter gases comprises, as main components, carbonmonoxide, hydrogen and in addition nitrogen.

A catalytic conversion is subsequently carried out with this synthesisgas to give higher alcohols, which is also denoted in the technicalliterature as “mixed alcohol synthesis” (see by way of example thereofWO 2008/048364 A2). This catalytic synthesis of the higher alcohols fromsynthesis gas can according to the invention be carried out, forexample, at reaction temperatures of 200° C. to 360° C., preferably attemperatures of 220° C. to 340° C., more preferably at 240° C. to 320°C., in particular at 260° C. to 300° C., for example at about 280° C. Inaddition, this reaction can be carried out, for example, at a reactionpressure of 10 bar to 110 bar, in particular at 30 bar to 90 bar,preferably at 50 bar to 70 bar, for example at about 60 bar.

In this synthesis, a product stream is obtained which is at atemperature for example in the abovementioned range and a high pressureof the abovementioned order of magnitude, so that this product stream ispreferably initially, for example by reduction in pressure in a turbine,converted to a manageable form. Electrical energy is recovered in thisreduction in pressure to a pressure of for example 5 bar to 15 bar, inparticular to about 10 bar, which energy can be used to meet most of theelectricity requirement of the process.

The composition of the product mixture obtained in this catalyticsynthesis of higher alcohols can vary strongly. The product mixturecomprises in particular alcohols, alkenes, alkanes, carbon monoxide andhydrogen from unconverted synthesis gas, carbon dioxide, nitrogen andmethane. The composition of the product phase depends on the compositionof the synthesis gas used, in particular the proportion of inert gasthereof (proportion of nitrogen), and the degree of conversion in thecatalytic reaction, through which results the remaining proportion ofcarbon monoxide and hydrogen and also possibly carbon dioxide and theratio of the products to the residual gas. Furthermore, the selectivityof the catalyst used determines the distribution of the desiredproducts, that is of the alcohols, alkenes, of the proportion ofalkanes, and also the proportion of gaseous byproducts, which areproduced in the reaction, in particular methane and carbon dioxide.

The synthesis gas not converted in the reaction is preferably led backto the stage before the conversion, so that amounts of hydrogen andcarbon monoxide present in this gas can be used in a renewed conversion.If the synthesis gas used comprises, for example, a proportion of 30% byvolume of nitrogen, which is inert with regard to the conversion sought,less unconverted synthesis gas has to be recycled than if the synthesisgas used comprises, for example, a proportion of 50% by volume ofnitrogen. If the proportion of nitrogen in the synthesis gas is lowerand amounts to, for example, only 10% by volume, it is possible, forexample, to separate nitrogen before the actual separation process usingan additional membrane.

The amount of absorption medium which is used in the first separationstage depends on the degree of conversion and accordingly on the productcomposition resulting therefrom. If a relatively large amount ofabsorption medium is used, more alkenes and alkanes are separated fromthe product mixture, but it is also to be considered though thatsimultaneously more undesirable gases, in particular nitrogen, carbondioxide, carbon monoxide and hydrogen, are coabsorbed.

Consequently, in the process according to the invention, through thefirst separation stage, which can also be denoted as gas-liquidseparation, initially a separation of the greater part of the gases, inparticular nitrogen, carbon monoxide, carbon dioxide, hydrogen andmethane, is achieved, since these gases are barely absorbed in theabsorption medium, the high boiling point hydrocarbon or hydrocarbonmixture. The gases separated can be lead back to the preceding processstage of the catalytic conversion of synthesis gas. Two liquid phasesare formed, namely an aqueous phase and an organic phase comprising theabsorption medium. Organic compounds which are regarded as usefulmaterials in the process according to the invention, in particularalcohols and alkenes and also alkanes, go predominantly into the organicphase, a lesser portion also into the aqueous phase. Short-chainalcohols, in particular methanol and ethanol, go predominantly into theaqueous phase. In a second separation stage, the aqueous phase isseparated from the organic phase of the absorption medium, preferably bydecanting. Subsequently, alcohols, alkenes and possibly alkanes aredesorbed from the absorption medium.

According to a preferred development of the process according to theinvention, the mixture obtained after the desorption, comprisingalkenes, possibly alkanes and possibly alcohols, is subsequentlyseparated through a first distillation into a fraction comprisingpredominantly the hydrocarbons and a fraction comprising predominantlythe alcohols.

This distillation is preferably carried out at an elevated pressure,which preferably is in a pressure range from about 10 bar to about 40bar.

According to preferred further development of the process according tothe invention, the hydrocarbons separated in the first distillation aresubsequently separated, in an extractive distillation with water, fromresidues of alcohol and water present in the hydrocarbons. Thisextractive distillation is also denoted in the present application, forthe purpose of differentiation, as second distillation. This seconddistillation is used for the further purification of the hydrocarbonsseparated previously. In this extractive distillation in a column, thehydrocarbons are obtained at the top of the column, while the water isalso partly obtained in the bottom of the column, alcohols stillgenerally being dissolved in this water. The product mixture from thebottom of the column is preferably led back in order for the alcoholspresent in the water to be recovered.

According to a preferred development of the process according to theinvention, alcohols, which are present in the aqueous phase after theseparation of the aqueous phase from the organic phase, preferably afterthe decanting, are separated from the water by distillation, thealcohols being obtained as an azeotrope with water at the top. Thisdistillation, which is used to recover additional alcohols from theaqueous phase, is also denoted, to better distinguish it from the otherseparation stages in the present patent application, as thirddistillation.

Preferably, the alcohols separated from the water in this thirddistillation are conveyed to the mixture obtained after the desorptionand, with this mixture, separated from the hydrocarbons through thefirst distillation. In this way, it is possible, in the firstdistillation which is used for the separation of the alcohols from thehydrocarbons, to recover a higher proportion of alcohols since eventhose alcohols are recovered which, in the decanting, went into theaqueous phase, without a separate distillation apparatus being necessaryfor this.

According to a preferred development of the invention, the alcoholfraction obtained in the first distillation, in which the alcohols areseparated from the hydrocarbons, subsequently preferably has waterremoved from it by means of a molecular sieve. The alcohol fraction can,after the first distillation, for example exhibit a water content withan order of magnitude of about 10% or less. In order to remove waterfrom the alcohol fraction, mention is made later still of alternativepossibilities to the removal of water by means of a molecular sievementioned here. After the removal of water, an alcohol mixture isobtained which comprises in particular methanol, ethanol, propanols andbutanols.

According to a preferred development of the process according to theinvention, this alcohol mixture obtained after the first distillationcan be subsequently separated, for example, through one or moreadditional distillation stages into alcohol fractions with each time adifferent number of carbon atoms, in particular into a C1 fraction, a C2fraction, a C3 fraction and a C4 fraction.

A possible variant of the process according to the invention providesfor alkenes present in the hydrocarbon mixture obtained after the firstdistillation, optionally after a further treatment, to be converted toalcohols by hydration. By this measure, the yield of alcohols obtainedin the process can on the whole be increased. In addition, there is theadvantage that alcohols can be separated better from alkanes, whilealkanes and alkenes, because of their chemical similarity, are difficultto separate.

The hydration of alkenes to give the corresponding alcohols is a knownreaction for the preparation of alcohols and is used industrially, forexample, for the production of isopropanol from propene. With theexception of ethene, the hydration of linear alkenes resultspredominantly in the formation of secondary alcohols. Isobutene ishydrated to give tertiary butanol, a tertiary alcohol.

There exist essentially two well-known industrial processes for thehydration of alkenes to give the corresponding alcohols; on the one handdirect hydration and alternatively indirect hydration.

In direct hydration, the alkene is reacted with water over an acidiccatalyst to give the respective alcohol. The hydration of alkenes togive alcohols is an equilibrium reaction. High pressures and lowtemperatures shift the equilibrium of the exothermic reaction to theproduct side in favor of the alcohols. The indirect hydration of alkenesis carried out in a two-stage reaction. The alkene is initially reactedwith sulfuric acid to give mono- and dialkyl sulfates and subsequentlyhydrolyzed to give the alcohol.

Industrially, ethanol is produced predominantly by fermentation ofcarbohydrates, for example of sugars from corn, sugar beet, grain orwheat. Synthetic ethanol can be produced from ethene by directhydration. The direct hydration of ethene is carried out in the gasphase over “solid” phosphoric acid (SPA catalysts), for example at250-300° C. and 50-80 bar. The hydration of ethene is an equilibriumreaction, in which high pressures and low temperatures favor theexothermic formation of ethanol. The indirect hydration of ethene is nolonger carried out industrially.

Various well-known processes are available for the direct hydration ofpropene: low-temperature/high-pressure processes (130-180° C., 80-100bar) with for example sulfonated polystyrene ion-exchange catalysts,high-temperature/high-pressure processes (270-300° C., 200 bar) with forexample reduced tungsten oxide catalysts and processes in the gas phase(250° C., 250 bar, WO₃—SiO₂ catalyst, ICI process/170-260° C., 25-65bar, phosphoric acid catalyst on SiO₂, Hüls process). The directhydration of propene with steam under high pressure is carried out inCanada, Mexico and Western Europe. In the indirect hydration of propene,it is also possible to use, besides propene, the C3 stream from refineryoffgas with a propene concentration of 40-60%.

2-Butanol (secondary butyl alcohol) can be produced from butene or MTBEraffinate by direct hydration or indirect hydration. 2-Butanol is usedfor the production of methyl ethyl ketone (MEK).

According to a first variant of the invention, the use of a catalystwith a high selectivity for alcohols and alkenes is preferred since arecovery of these product families as useful materials is in theforeground, while the formation of alkanes and also oxygenatedcompounds, such as aldehydes, esters, ethers, carboxylic acids and thelike, which are obtained on using Fischer-Tropsch catalysts often inhigher proportions, is not desired in the process according to theinvention. Furthermore, the subsequent separation processes in thetreatment of the product mixture after the conversion of the synthesisgas become more expensive as the product mixture becomes more complex.In the conversion of synthesis gas using Fischer-Tropsch catalysts, thisis less problematic since the product mixtures are often not separatedinto individual families but the mixture is used as such as additive infuels.

The synthesis of higher alcohols generally provides a mixture of primaryalcohols. Through the inclusion of hydration in the process, it ispossible to selectively form secondary alcohols and accordingly to widenthe product spectrum. A more uniform product is thus produced from thecomplex product mixture, which leads to advantages in the purificationprocess and in marketing logistics.

For the process according to the invention, not only smelter gases butalso any other suitable synthesis gas sources are suitable in principle.By using smelter gases, the process according to the invention has themerit that a high proportion of nitrogen frequently present in thesmelter gases can be satisfactorily separated by the separation stage ofthe absorption in a high boiling point hydrocarbon or hydrocarbonmixture. Nitrogen as inert gas in the present process absolutely has tobe separated since a high proportion of nitrogen would make moredifficult the subsequent treatment of the product mixture.

In the context of the present invention, an overall process has beendeveloped which makes it possible to produce higher alcohols (with twoor more carbon atoms) with good yield starting from synthesis gas. Inthe present application, processes are described which, starting fromthe product mixture obtained in the conversion of synthesis gas,comprising carbon monoxide and/or carbon dioxide and hydrogen, offeradvantages economically, technologically and/or ecologically comparedwith known processes, in particular as regards simply a separation withsubsequent individual marketing of the products/substance groups. Inthis connection, particular attention was paid to the optimization ofthe product separation in harmony with the synthesis stages. Thisrelates inter alia to the respective physical process conditions(pressure, temperature) and also to the establishment of preferred ortechnically tolerable reactant ratios for the synthesis stages whileconsidering in particular economic circumstances.

Due to the large plant capacities which are necessary for example forthe utilization of significant amounts of smelter gas but also withother synthesis gas sources, use is preferably made of processes whichlead to products with sufficiently large (potential) markets. It isaccordingly particularly advantageous here to consider commoditychemicals which can be used, for example, in the plastics or fuelssectors.

According to a possible preferred variant of the process according tothe invention, from the first mixture of alkanes, alkenes and alcoholsobtained after the catalytic conversion of synthesis gas and preferablyafter separation of the unconverted synthesis gas, initially the alkanesand alkenes are separated from the alcohols and only then are thealkenes hydrated in this second mixture.

The alcohols can be separated from the alkenes and alkanes at littlecost. In comparison, the alkenes can be separated from the alkanes onlyat considerable cost. The consecutive hydration of the alkenes to givealcohols accordingly facilitates the operation of separating alkenes andalkanes.

The separation of the alkene/alkane mixture into the individual Cx cutsor alkenes can optionally also be advantageous since this makes possiblethe separate hydration of the individual alkenes. Alkenes, therespective hydration products of which are particularly suitable for thefuel market, or alkenes which can be hydrated under mild reactionconditions or inexpensively, can be selectively converted to therespective alcohols. Alkenes for which there is an appropriate alkenemarket can be separated from the respective C cut and marketed.Furthermore, the reaction conditions for the hydration of the individualCx cuts or alkenes can be chosen independently of one another. Forexample, a hydration of the C2 cut or of ethene could be dispensed withand the ethene could instead be used for other applications in thechemical industry. Moreover, in this way a relatively pure alkane streamcan be obtained which can be used for the production of synthesis gas orthe generation of energy. With this way of proceeding though, a separateplant for the hydration of the alkenes is required for each C cut or abatchwise hydration of the different fractions must be carried out.

According to an alternative preferred variant of the process accordingto the invention, the second mixture comprising the alkanes and alkenescomprises a mixture of C2-C4 alkenes or a mixture of C2-C5 alkenes whichis subsequently hydrated in the mix to give the corresponding alcohols.Consequently, in this variant, the hydration of an alkane/alkene mixtureis carried out without providing beforehand a separation of this mixtureinto different fractions with different numbers of carbon atoms.

With regard to the reaction conditions for the hydration of such analkene/alkane mixture, it must be taken into consideration that theconventional industrial processes are optimized for the conversion ofthe individual alkenes and differ from one another in the choice of thecatalyst and of the reaction conditions. For this stage of the hydrationof the alkene/alkane mixture, therefore preferably process conditionsare to be used in this variant which make possible the conversion of allalkenes or promote the conversion of the favored alkenes to therespective alcohols. As regards the abovementioned process variant, thehydration of the alkene mixture offers the advantage that merely oneplant is required for the hydration or a batchwise hydration of thevarious fractions can be dispensed with.

After the hydration, the alkanes are separated from the alcohols formed.The alkane stream remaining after the separation of the alcohols canthen be used, for example, for the production of synthesis gas orenergy.

According to a preferred further development of the process according tothe invention, the conditions for the hydration of the alkane/alkenemixture with regard to the choice of the catalyst and of the reactionconditions, in particular of the temperature and pressure, at which thehydration reaction is carried out, are chosen such that the hydration ofpropene and/or 1-butene is favored over that of ethene. It wasestablished that, with the catalysts which were used in the context ofthe present invention in the production of higher alcohols by catalyticconversion of synthesis gas, predominantly propene is formed as alkene.As a rule, the CO selectivity of the conversion of synthesis gas to thealkenes decreases in the order 1-propene>1-butene>ethene. The industrialprocesses for the hydration of 1-propene and 1-butene proceed undermilder reaction conditions than those of ethene so that in this processvariant it might optionally be advantageous to concentrate on thehydration of propene and to neglect the hydration of ethene oroptionally to dispense with the hydration of ethene.

According to a preferred further development of the process according tothe invention, the direct hydration is carried out at elevatedtemperatures and at elevated pressure. Wide temperature ranges and widepressure ranges are in principle possible here, depending on which otherconditions are selected. The hydration is as a rule carried out in thepresence of an acid acting as catalyst.

For example the hydration of the alkenes can be carried out attemperatures above 80° C., in particular above 100° C., for example attemperatures in the range from 100° C. to 180° C., preferably at 120° C.to 150° C., and/or at a pressure of 5 bar to 150 bar, in particular at apressure of 10 bar to 100 bar, preferably at a pressure of 50 bar to 100bar, for example at a pressure of 70 bar to 80 bar. The hydration ofpropene and of 1-butene proceed under similar reaction conditions eachtime, for example at the abovementioned temperatures and pressures. Inthe industrial direct hydration of propene, conversions of for exampleup to about 75% per pass are achieved. For the direct hydration of thealkene/alkane mixture, the invention therefore proposes to be guided bythe reaction conditions of the hydration for propene and 1-butene. It isalso conceivable in principle to carry out the hydration of thealkene/alkane mixture in several consecutive reactors with differentcatalysts and/or different reaction conditions and separation atintervals of the alcohols formed.

A third possible preferred variant of the process according to theinvention provides for carrying out the hydration of the alkenes withthe mixture of alkanes, alkenes and alcohols without the alcohols beingseparated from this mixture beforehand. The hydration of the alkenes inthe mixture of alcohols, alkenes and alkanes obtained in the conversionof the synthesis gas, without preceding separation of the alcoholspresent in this mixture, can, for example, offer the advantage that thereaction mixture is already at a comparatively high pressure of forexample about 60 bar and therefore merely has to be preheated to thereaction temperature.

At a reaction temperature of for example about 150° C., the hydration ofthe alkenes to the alcohols is thermodynamically preferred. Experimentsin the context of the synthesis of the higher alcohols with specificcatalysts and subsequent hydration and also calculations for anequilibrium reactor clearly show that, on carrying out the hydration atelevated temperature (for example of up to 150° C.) and an elevatedpressure of for example from 2 bar to 100 bar, a conversion of thealkenes and of the primary C₃₊ alcohols to the secondary alcohols takesplace. In particular, propene and 1-butanol are converted predominantlyto isopropanol and 2-butanol. Ethene is hydrated to give ethanol.

According to a preferred further development of the process according tothe invention, after the hydration, the alkanes are separated from theproduct mixture obtained and the remaining mixture of alcohols isoptionally purified and/or separated into individual fractions ofalcohols or individual alcohols. In turn, the advantage exists here thatin principle only alcohols and alkanes are present after the hydration,even in the variant described above in which the alcohols alreadyobtained in the conversion of the synthesis gas in the first stage arenot separated before the second stage of the hydration. Accordingly, inturn, only two substance classes are present in the mixture, which caneasily be separated from one another, while the separation of alkenesand alkanes would be substantially more difficult.

According to the process according to the invention, the stage isprovided, preferably before the hydration of the alkenes to give thecorresponding alcohols and after the catalytic conversion of thesynthesis gas, in which the product mixture obtained in this reaction isseparated into a gas phase and a liquid phase, the liquid phase beingused for the subsequent hydration of the alkenes to give the alcohols.The gas phase separated at this point can for example compriseunconverted CO and H₂ and also CO₂, CH₄ and N₂. The gas phase obtainedin this separation operation, which as a rule comprises the unconvertedgases mentioned, can, according to a preferred variant of the processaccording to the invention, be at least partially led back to the stageof the catalytic conversion of the synthesis gas in order in this way toincrease the yield of the overall process through the renewed conversionof the recycled reactant gases to higher alcohols.

Alternatively to this, it is also possible in principle to carry out thehydration of the alkenes before a separation of the product mixtureobtained after the conversion of the synthesis gas into a gas phase anda liquid phase. In this case, the hydration is carried out for exampledirectly in a reactor arranged downstream of the synthesis of higheralcohols and without preceding separation of the product mixture.Propene and butene can for example be hydrated at about 150° C. whilehigher temperatures of for example about 230° C. to 260° C. areadvantageous for the hydration of ethene. The hydration can be carriedout at a lower temperature than the preceding conversion of thesynthesis gas, it being possible for temperatures of for example 120° C.to 150° C. to be selected for the hydration. It can therefore beadvantageous to cool the product mixture for the hydration totemperatures of this order of magnitude.

Experiments, calculations and the simulation of the synthesis of higheralcohols with subsequent hydration show that, under the reactionconditions of the synthesis of higher alcohols, the dehydration of thealcohols to give the alkenes is thermodynamically preferred. When thereaction conditions of the synthesis of higher alcohols are for exampleabout 280° C. and about 60 bar, a virtually complete conversion of thealcohols into the corresponding alkenes is possible.

At a reaction temperature of the order of magnitude of for example about50° C., the hydration of the alkenes to give the alcohols is, incomparison, thermodynamically preferred. Experiments in the context ofthe synthesis of the higher alcohols with specific catalysts andcalculations or simulations of the subsequent hydration for anequilibrium reactor clearly show that, on carrying out the hydration atfor example about 50° C. and a pressure of about 60 bar, a conversion ofthe alkenes and of the primary alcohols to the secondary alcohols takesplace. In particular, propene and 1-butanol are converted predominantlyto isopropanol and 2-butanol. Ethene is hydrated to give ethanol.

However, it should be taken into consideration, in this purelythermodynamic analysis, that the industrial processes for hydration as arule are carried out at reaction temperatures of 130-260° C. It cantherefore be assumed that the reaction at 50° C. proceeds at a markedlyreduced reaction rate. This process variant is therefore less suitablefor the hydration of the alkenes (or can be carried out only undercertain circumstances).

Instead, preference is consequently to be given to one of theabovementioned variants in which initially, after the synthesis ofhigher alcohols, the separation into a gas phase and a liquid phase iscarried out, the product mixture being cooled after the synthesis ofhigher alcohols from the synthesis gas.

In the process according to the invention, there are in particular thethree preferred process variants subsequently mentioned:

In variant 1, the process preferably comprises the stages of:

-   -   production of higher alcohols (with at least two carbon atoms)        and of alkenes by catalytic conversion of synthesis gas;    -   separation of the product mixture obtained into a gas phase and        a liquid phase;    -   separation of the liquid phase into an aqueous and an organic        phase;    -   desorption of the alkenes, possibly of the alcohols and possibly        of the alkanes from the absorption medium;    -   separation of the alkenes and possibly of the alkanes formed as        byproducts from the alcohols obtained;    -   optionally purification of the alcohol mixture separated from        the alkenes and alkanes into individual compounds or groups of        compounds, in particular ethanol, propanols, butanols and        possibly methanol;    -   separation of the mixture of alkenes and alkanes into several        fractions with each time a different number of carbon atoms, in        particular C2, C3 and C4 fraction;    -   each time separate hydration of the fractions obtained        previously, preferably by reaction with water, each time        mixtures of alcohols and alkanes with the same number of carbon        atoms being obtained;    -   optionally purification of the respective mixtures of alcohols        and alkanes with the same number of carbon atoms into individual        alcohols and alkanes.

In variant 2, the process preferably comprises the stages of:

-   -   production of higher alcohols (with at least two carbon atoms)        and of alkenes by catalytic conversion of synthesis gas;    -   separation of the product mixture obtained into a gas phase and        a liquid phase;    -   separation of the liquid phase into an aqueous and an organic        phase;    -   desorption of the alkenes, possibly of the alcohols and possibly        of the alkanes from the absorption medium;    -   separation of the alkenes and possibly of the alkanes formed as        byproducts from the alcohols obtained;    -   optionally purification of the alcohol mixture separated from        the alkenes and alkanes into individual compounds or groups of        compounds, in particular ethanol, propanols, butanols and        possibly methanol;    -   hydration of the mixture of the alkenes and alkanes previously        separated from the alcohols, preferably by reaction of the        alkenes with water, a mixture of alcohols and alkanes being        obtained;    -   separation of the alkanes from the mixture after the hydration        and optionally combination of the alcohols thus obtained with        the alcohols previously obtained in the synthesis;    -   optionally purification of the alcohol mixture obtained into        individual compounds or groups of compounds, in particular        ethanol, propanols, butanols and possibly methanol.

In variant 3, the process preferably comprises the stages of:

-   -   production of higher alcohols (with at least two carbon atoms)        and of alkenes by catalytic conversion of synthesis gas;    -   separation of the product mixture obtained into a gas phase and        a liquid phase;    -   separation of the liquid phase into an aqueous and an organic        phase;    -   desorption of the alkenes, possibly of the alcohols and possibly        of the alkanes from the absorption medium;    -   hydration of the product mixture obtained previously from the        organic liquid phase comprising alcohols, alkenes and alkanes,        preferably by reaction with water, the alkenes in the mixture        being hydrated to give the corresponding alcohols;    -   separation of the alkanes from the alcohols obtained;    -   optionally purification of the alcohol mixture separated from        the alkanes into individual compounds or groups of compounds, in        particular ethanol, propanols, butanols and possibly methanol.

Alternatively to this, a fourth process variant is possible in which thehydration of the alkenes is already carried out after the conversion ofthe synthesis gas and before the separation of the product mixtureobtained into a gas phase and a liquid phase.

In variant 4, the process preferably comprises the stages of:

-   -   production of higher alcohols (with at least two carbon atoms)        and of alkenes by catalytic conversion of synthesis gas;    -   hydration of the product mixture obtained comprising alcohols,        alkenes and alkanes, the alkenes in the mixture being hydrated        to the corresponding alcohols;    -   separation of the product mixture obtained into a gas phase and        a liquid phase;    -   optionally separation of the liquid phase into an aqueous and an        organic phase;    -   optionally desorption of the alcohols, possibly of the alkenes        and possibly of the alkanes from the absorption medium;    -   separation of the alkanes and possibly of the alkenes present        from the alcohols obtained;    -   optionally purification of the alcohol mixture separated from        the alkanes into individual compounds or groups of compounds, in        particular ethanol, propanols, butanols and possibly methanol.

In all four of the abovementioned process variants, an at least partialrecycling of the gas phase to the synthesis of the higher alcohols afterthe gas-liquid separation is advantageous.

Besides the abovementioned process variants, it is also possible tocarry out the hydration of the alkenes by a combination of two or moreof the abovementioned process variants. For example, the composition ofthe product mixture of higher alcohols (with at least two carbon atoms)and alkenes initially obtained by catalytic conversion of synthesis gascan be shifted by process variant 4 and, after separation of the productmixture then obtained into a gas phase and a liquid phase, the alkenespresent in the liquid phase are hydrated for example by means of one ofthe process variants 1, 2 or 3 to give the corresponding alcohols. Thecombination of the two process variants can for example favor theisomerization of the primary alcohols to give secondary alcohols. Theisomerization of the primary alcohols to give the secondary alcoholsproceeds via the dehydration of the primary alcohols to give thecorresponding alkenes as intermediate products. The dehydrationpreferably proceeds at higher temperatures than the hydration.

The provision of the synthesis gas for the catalytic conversion toalcohols according to the invention can comprise, besides thepreparation of the synthesis gas, also the purification and theconditioning of the synthesis gas. Both fossil fuels, such as naturalgas, coal, but also CO- and CO₂-rich gases, for example from steel orcement works, and hydrogen, can be used as feed.

It is also possible to obtain the synthesis gas used from biomass. Thehydrogen is preferably produced in a sustainable manner by means ofrenewable energy sources and/or low CO₂ emissions, for example by waterelectrolysis or methane pyrolysis. The electricity for operating thehydrogen production is preferably generated using renewable energysources.

The liquid phase comprises predominantly the alcohols, alkenes andpossibly alkanes formed. Reducing the pressure to less than 50 bar, inparticular to less than 30 bar, preferably to less than 20 bar, morepreferably to less than 10 bar, for example from 3 to 1 bar, preferablyto about 1 bar, makes it possible for example to evaporate the alkenesand alkanes and to separate them from the product mixture. However,other methods known to a person skilled in the art for the separation ofalkenes and alkanes from alcohols are likewise suitable here. It isoptionally advantageous, for economic and/or ecological optimization ofthe process, to convert the alkanes into synthesis gas, for example viaa partial oxidation, steam reforming or autothermal reforming, and tolead back into the process. The alkanes can optionally also bedehydrogenated to give the corresponding alkenes and subsequentlylikewise hydrated in order to increase the yield of alcohols. Thealcohols remain in the liquid phase and, after separation of the waterformed as connected product, are optionally marketed as product mixture,for example as fuel additive, or separated in a distillation into theindividual alcohols.

Furthermore, there exists the option of hydrating the alkenes after theseparation of the alkanes from the respective Cx cuts. This gives theadvantage of a comparatively pure reactant concentration and thepossibility of carrying out the hydration under conditions well-knownindustrially for the respective alkene. Due to the expenditure onequipment and energy of the separation of alkanes and alkenes, thisoption though can only be carried out under certain circumstances.

The various options for integration of the consecutive conversion of thealkenes to alcohols into the process concept for the synthesis of higheralcohols differ each time in the composition of the reaction mixture andthe prevailing process conditions, such as temperature and pressure, andalso in the manner and time of the separation of the alcohols, alkenesand alkanes from the synthesis gas. The possibility exists, through theintegration of the hydration of the alkenes into the process concept forthe synthesis of higher alcohols, of using the already existingtemperature and pressure levels of the catalytic synthesis of higheralcohols for the hydration.

Preferably, primary alcohols are formed in the catalytic synthesis ofhigher alcohols from synthesis gas. The formation of secondary alcoholsis hardly observed. In comparison, the hydration of linear alkenespreferentially results in the formation of secondary alcohols, such asisopropanol and 2-butanol (with the exception of ethanol). The synthesisof higher alcohols and the consecutive hydration of the alkenestherefore differ in their product spectrum.

If the isomerization of primary alcohols to give secondary alcohols isdesired, a suitable process concept is to be selected for it whichguarantees the isomerization of primary alcohols to give secondaryalcohols.

Due to the possible isomerization of the primary alcohols to givesecondary alcohols, a separation of the alcohols from the hydrocarbonmixture (alkenes, alkanes) presents itself, i.e. the abovementionedprocess variants 1 and 2 preferably present themselves for thehydration. The alcohols can be separated from the alkenes and alkanes atlittle cost. In comparison, the alkenes can be separated from thealkanes only at considerable cost. The consecutive hydration of thealkenes to give alcohols accordingly facilitates the operation ofseparating alkenes and alkanes.

According to a preferred further development of the process according tothe invention, the hydrocarbon mixture obtained after the firstdistillation is separated into fractions with each time the same numberof carbon atoms, in particular into a C3 fraction, a C4 fraction and aC5 fraction.

According to a possible variant of the process according to theinvention, the removal of water from the alcohol fraction can be carriedout by, from the alcohol fraction obtained in the first distillation,separating the lower alcohols methanol and ethanol in a column with alittle water, and the remaining alcohol mixture is treated with a higherhydrocarbon and is separated in a decanter into an organic phase and anaqueous phase. In this process variant, it can be advantageous to use acomparatively large amount of the higher hydrocarbon as absorptionmedium; accordingly, most of the alcohols go into the organic phase. Theaqueous phase can be sent back to the abovementioned decanter fortreatment.

Preferably, the alcohols are stripped out from the organic phase in anadditional column and residual water present in the alcohols issubsequently removed using a molecular sieve.

According to an alternative variant of the process according to theinvention, from the alcohol fraction obtained in the first distillation,the lower alcohols methanol and ethanol are separated from the higheralcohols in an extractive distillation with a hydrophilic substance, inparticular with ethylene glycol, the higher alcohols are subsequentlyseparated from the hydrophilic substance in an additional distillationcolumn and water present in the higher alcohols is then optionallyremoved as azeotrope.

According to an alternative variant of the process, from the alcoholfraction obtained in the first distillation, the water can also beselectively removed for example by pervaporation through a membrane andbe withdrawn as permeate in vapor form.

Finally, according to a further alternative variant of the process, fromthe alcohol fraction obtained in the first distillation, the water canalso be removed for example by azeotropic distillation with a selectiveadditive, in particular with a higher hydrocarbon, preferably withbutane or pentane.

Mention has already been made above that a principal concern of thepresent invention consists in recovering the useful materials present inthe product mixture obtained after the catalytic conversion of thesynthesis gas, in particular the alcohols and alkenes being supposed tobe recovered here. Accordingly it is preferably sought according to theinvention for at least the alcohols methanol, ethanol, propanol andbutanol, and also the C4 olefins and C5 olefins and possibly C3 olefinsand C2 olefins, to be recovered from the material mixture obtained afterthe catalytic conversion of synthesis gas.

Various substances are suitable for the absorption medium which is usedin the separation stage for the separation of the inert gases from theproduct stream. Preferably, the high boiling point hydrocarbon used asabsorption medium or the hydrocarbon mixture comprises a diesel oil oran alkane, in particular a dodecane, with a viscosity of less than 10mPas at ambient temperature and/or a boiling point of more than 200° C.

Preferably, the subsequent desorption of the alkenes, possibly alcoholsand possibly alkanes from the absorption medium is carried out in adistillation column, preferably at a pressure of 1 bar to 5 bar.

According to an advantageous further development, after the desorption,the absorption medium is led back after heat exchange into theseparation stage of the absorption.

Preferably, the gas phase of the gases not absorbed in the absorptionmedium, which gas phase is separated from the product mixture after thecatalytic conversion of the synthesis gas, comprises at least the gasesnitrogen, hydrogen, carbon monoxide, carbon dioxide and methane.

Mention has already been made above that alkenes present in thehydrocarbon mixture obtained after the first distillation according toan optional variant of the process according to the invention,optionally after a further treatment, can be converted by hydration toalcohols, in order in this way to increase the proportion of alcohols inthe product mixture and to simplify the separation of the productfamilies. For example, such a hydration of the reaction mixtureconsisting of alcohols, alkenes and alkanes can be carried out at atemperature of about 150° C. As can be demonstrated from simulations andcalculations of the thermodynamic equilibrium, the mixture of alkenesand primary alcohols is, under these reaction conditions, virtuallycompletely converted to secondary alcohols. The isomerization of theprimary alcohols to the secondary alcohols presumably takes place viathe formation of the alkenes as intermediates. The hydration of theproduct mixture of the synthesis of higher alcohols from alcohols andalkenes accordingly offers the possibility of shifting the productspectrum in the direction of the secondary alcohols. The industrialhydration of propene and 1-butene proceeds at reaction temperatures offor example 120 to 150° C.

The consecutive hydration of the alkenes formed as byproducts in thecatalytic synthesis of higher alcohols makes it possible, with suitablereaction management, to increase the alcohol yield. Furthermore, thisequilibrium reaction offers the possibility, in principle, of convertingthe complex reaction mixture of primary alcohols and alkenes tosecondary alcohols (with the exception of ethanol) by means ofdehydration and hydration stages. The reduction in the products resultsin a small number of stages of purification of the individual productsand facilitates the marketing of the products of the synthesis of higheralcohols.

The present invention is described in more detail below on the basis ofexemplary embodiments with reference to the enclosed drawings. In thisconnection:

FIG. 1 shows a simplified diagrammatic representation of an exemplaryseparation process for the treatment and separation of a gaseousmaterial mixture which was obtained by catalytic conversion of synthesisgas.

Subsequently, a description is given, with reference to the simplifiedreaction scheme according to FIG. 1, by way of example of a possibleprocess for the separation of a product mixture obtained in thecatalytic conversion of synthesis gas. The exemplary process describedbelow for the separation describes the separation from the gas phase ofthe mixture of alcohols, alkenes and alkanes obtained by the conversionof the synthesis gas and its subsequent separation into a mixture ofalcohols and a mixture of hydrocarbons. On using the different processvariants and converting the product mixture obtained, the individualstages of this process for the separation of the product mixture can bevaried and be adapted to the product mixture obtained after theconversion.

Removal of Inert Gas and Gas-Liquid Separation

After the catalytic conversion of a synthesis gas stream under theconditions of the process according to the invention, a product streamis present at a temperature of 280° C. and a pressure of 60 bar. Thelatter is initially reduced in a turbine (not represented in FIG. 1) toa pressure of 5 to 20 bar, preferably to about 10 bar, electrical energybeing recovered which can be used for the electricity requirement of theprocess.

The subsequent gas-liquid separation is used in particular for theseparation of the inert gases (nitrogen) and unconverted components ofthe synthesis gas (hydrogen, carbon monoxide and possibly carbondioxide, and also the byproducts carbon dioxide and methane) and iscarried out by introducing the crude product gas stream 10 into anabsorption apparatus 11, in which the absorption of the product streamin a diesel oil (reference component dodecane) or alternatively in analkane or a hydrocarbon mixture with a comparatively low viscosity offor example less than 10 mPas at ambient temperature and with preferablya comparatively high boiling point of in particular more than 200° C. iscarried out. The water is in this connection not absorbed but for themost part condensed as second liquid phase. The separated abovementionedgaseous components can be led back via the line 12 to the catalyticconversion of the synthesis gas (not represented here) and be convertedthere once again.

The two liquid phases (organic phase and aqueous phase) obtained in thisabsorption operation, which can be carried out at a pressure of forexample about 10-20 bar, can subsequently be separated in a decanter 13,little of the hydrocarbons but a portion of the alcohols going into theaqueous phase. The separation of the two liquid phases in the decanter13 can for example likewise be carried out still at the abovementionedpressure of about 10-20 bar. The organic phase separated in thisconnection comprises the hydrocarbons, at least a portion of thealcohols, the absorption medium, possibly a portion of the water andalso possibly amounts still remaining of inert and unconverted gases, inparticular nitrogen and carbon monoxide, and is led to a desorptionapparatus 15, via a line 14, in which the alcohols and hydrocarbons aredesorbed from the absorption medium for example at low pressure, forexample at a pressure of about 1 bar, and a bottom temperature of 216°C. A column, for example, can be used as desorption apparatus 15. Withrelatively low amounts of inert gases in the product stream of thecatalytic conversion of synthesis gas, a condensation of the low boilingpoint components may alternatively also be suitable. The absorptionmedium (dodecane, diesel oil) can be led back to the absorptionapparatus 11 via the line 16.

Separation of Alcohols/Hydrocarbons

The organic phase desorbed from the absorption medium in the desorptionapparatus 15, which comprises the alcohols, hydrocarbons, small amountsof water and possibly amounts of unconverted and inert gases, issubsequently conveyed via a line 18 to a first distillation column 17.The separation of alcohols and hydrocarbons is carried out bydistillation in this first column, preferably at a high pressure of forexample 10 bar to 40 bar, for example at about 36 bar, and a bottomtemperature of for example 221° C., so that the C3 constituents remainstill condensable even in the presence of inert gas residues possiblypresent. This separation is preferably operated in such a way that thehydrocarbons are virtually completely removed from the alcohol fractionat the bottom, while relatively small contents of alcohol (in particularmethanol) can be tolerated in the hydrocarbons. This process canoptionally be assisted by a solubility-driven membrane. The alcoholsobtained in this first distillation, which still comprise a proportionof water, can be withdrawn from the first distillation column 17 via theline 19 from the bottom and dried, as is more fully explainedsubsequently.

Preparation of the Hydrocarbons

The hydrocarbons obtained in the first distillation column 17 at the topcan be conveyed, via a line 20, to a second distillation column 21, inwhich they are recovered at elevated pressure of preferably 5 bar to 20bar, for example at a pressure of about 10 bar, and a bottom temperatureof 102° C. at the top of the distillation column 21, and can bewithdrawn, via the product line 22, for further purification andoptionally separation into individual carbon fractions (not representedin FIG. 1). The alkanes possibly present in the product stream 22 ofhydrocarbons can be separated from the alkenes, by preferably carryingout a hydration of the alkenes, so that these are converted to alcohols,which then can be separated comparatively simply from the alkanes, forexample by distillation.

The remaining water and also the alcohols dissolved therein are obtainedin the bottom of this second distillation column 21. This stream isseparated and can be led back, via the line 23, for the recovery of thealcohols in a third distillation column 24. The condenser of the columncan, for example, be a partial condenser. The outputs of the column area gas phase of hydrocarbons and inerts, a liquid phase of hydrocarbonsand also an aqueous phase which can be returned to the column as reflux.

The aqueous phase separated from the organic phase in the decanter 13 isconveyed, via the line 28, to the third distillation column 24, whichaqueous phase can comprise amounts of the alcohols since these are atleast partially soluble in water, in particular the lower alcohols, suchas methanol and ethanol. The distillation in this third distillationcolumn 24 can, for example, be carried out at a pressure of about 2 barand at a temperature in the bottom of, for example, about 120° C. Thealcohols present in this aqueous fraction are recovered at the top ofthe third column and conveyed, via the line 29, to the firstdistillation column 17 and combined there with the mixture of alcoholsand hydrocarbons from the organic phase, so that these alcoholsrecovered from the aqueous phase can be separated in the firstdistillation column 17 with the rest of the alcohols and subsequently,for example, dried via the molecular sieve 25. The water separated inthis third distillation column can, for example, be withdrawn from theplant via the line 30 as wastewater.

In this way, the useful materials, alkenes and alcohols, can berecovered each time as separate product groups by means of theseparation scheme represented in exemplary and simplified fashion inFIG. 1 from the crude gas product mixture 10 through absorption in ahigh boiling point hydrocarbon or hydrocarbon mixture, subsequentdecanting for the phase separation and subsequent repeated distillation.

Removal of Water from the Alcohol Fraction

The alcohol fraction from the first distillation column 17 can have awater content of for example about 10%. This water can, for example, beremoved using a molecular sieve 25. In this process variant, thealcohols are conveyed, via the line 19, to the molecular sieve 25, bymeans of which water is removed from them, it being possible for thewater to be withdrawn from the plant via the line 26. The alcohols driedin this way can be withdrawn via the product line 27 and optionallyfurther separated, for example into individual carbon fractions(isomeric alcohols with each time the same number of carbon atoms) orinto individual specific alcohols.

Suitable as alternative method for removing the water from the alcoholfraction is extractive distillation, for example with ethylene glycol,which however requires a further separation stage since the water ispulled from the ethylene glycol into the bottom while the alcoholsmethanol and ethanol proceed via the top virtually free from water.About half of the propanol and all of the butanol remain in the bottomand these C3-C4 alcohols must likewise be removed via the top from theethylene glycol in a subsequent column.

Pervaporation is possible as third alternative. In this connection,water passes selectively through a membrane and is withdrawn as permeatein vapor form. The energy consumption is even lower than in a molecularsieve.

A further alternative method would be an azeotropic distillation, forexample with butane or pentane as selective additive.

Examples for the Composition of the Product Mixture Obtained After theCatalytic Conversion of the Synthesis Gas

In the context of the present invention, it has been investigated howthe variation in different parameters has an effect on the compositionof the gaseous material mixture obtained after the catalytic conversionof the synthesis gas. The results are reproduced in the followingexamples.

EXAMPLE 1

The following example 1 gives an exemplary product composition which wasobtained in the catalytic conversion of synthesis gas according to theprocess according to the invention. The catalyst used exhibited a highC2-C4 selectivity, alcohols, alkenes and alkanes being formed. Acatalyst which comprises grains of nongraphitic carbon with cobaltnanoparticles dispersed therein was used. The CO selectivity with regardto the conversion to alcohols is about 28% and the CO selectivity withregard to the conversion to alkenes is about 32%. The precise COselectivities of the catalytic conversion of the synthesis gas areapparent from the following table 1. The selectivities given in table 1were normalized to the products detected in the catalytic tests (C1-C5alcohols, C1-C5 alkenes and C1-C5 alkanes, CO₂). The analysis of the COconversion allows it to be concluded therefrom that, besides namedproducts detected, long-chain C₆₊ alcohols, C₆₊ alkenes and C₆₊ alkanes,and also possibly aldehydes, are also formed.

TABLE 1 CO Selectivity CO₂ 9.8% Methane 17.9%  Ethane 4.6% Propane 4.3%Butane 3.0% Pentane 0.3% Ethene 6.0% 1-Propene 15.1%  1-Butene 7.2%1-Pentene 4.2% Methanol 3.7% Ethanol 4.6% 1-Propanol 1.1% 1-Butanol18.3%  Alkanes (C2-C5) 12.2%  Alkenes (C2-C5) 32.5%  Higher alcohols24.0% 

A pulverulent catalyst was used in this example. The catalyst canalternatively also be pressed into tablets, for example.

Table 1 above shows that, in the catalytic conversion of the synthesisgas according to the invention, a comparatively high proportion ofalcohols compared with the alkenes can be obtained if a suitablecatalyst is used. The proportion of alkanes in the product mixture islower in comparison thereto. The alkenes can likewise be converted toalcohols in the following hydration stage so that, inclusive of thefollowing hydration stage, the synthesis gas can be converted overallinto alcohols with a CO selectivity of virtually 60%, primary alcohols(methanol, ethanol, 1-propanol and 1-butanol) being obtained from thealcohol synthesis and ethanol and secondary alcohols (2-propanol,2-butanol and possibly 2-pentanol) being obtained from the hydrationstage and the methanol content being comparatively low. Such an alcoholmixture is suitable, for example, as fuel additive for blending withgasoline. The separation into the individual alcohols is alternativelypossible.

For comparison, a CO_(0.126)Mo_(0.255)C catalyst was used, as describedin the US document US 2014/0142206 A1 in Example 2. The H₂ to CO ratioin the synthesis gas was 1:1. After the conversion of the synthesis gas,a composition according to the following table 1a was obtained.

TABLE 1a CO Selectivity CO₂  3.80% Methane  1.27% C2-C6 hydrocarbons1.0% Methanol 26.21% Ethanol 30.70% 1-Propanol 33.60% 1-Butanol  2.00%Higher alcohols 3.8%

The above table 1a shows that, on using this catalyst, predominantlyalcohols are formed, the proportion of methanol being comparatively highwhile only a little 1-butanol is formed. C2-C6 hydrocarbons are onlyformed in small amounts.

For further comparison, a catalyst with high selectivity for olefins wasused, as described in Example 2 of U.S. Pat. No. 4,510,267 A. After theconversion of the synthesis gas, a composition according to thefollowing table 1b was obtained. The composition of the synthesis gaswas in this case H₂:CO=1:1. The selectivities (% by weight) given inU.S. Pat. No. 4,510,267 A and in table 1b were recalculated in COselectivities for comparison with the results in Table 1 and for thesimulation of the separation process. The selectivity for CO₂ wasdetermined from the difference from 100% and the sum of all products.For the simulation of the separation process, the C₁₁₊ alkanes and theC₁₁₊ alkenes were assumed to be undecane or undecene.

TABLE 1b % by weight CO Selectivity Methane 12.3%  11.96% Ethane 0.9%0.93% Propane 1.4% 1.49% Butane 1.5% 1.61% Pentane 1.1% 1.19% Hexanetraces 0.00% Heptane 0.8% 0.87% Octane 0.6% 0.66% Nonane 0.3% 0.33%Decane 0.4% 0.44% C₁₁₊ Alkanes 2.4% Undecane (assumption) — 2.63% Ethene7.7% 8.56% Propene 15.2%  16.90% Butene 11.9%  13.23% Pentene 7.8% 8.67%Hexene 6.7% 7.45% Heptene 4.0% 4.45% Octene 2.4% 2.67% Nonene 1.7% 1.89%Decene 1.3% 1.45% C11+ Alkenes 6.5% Undecene (assumption) — 7.23%Methanol — 0.00% Ethanol 2.4% 1.62% CO₂ — 3.79% Total 100.00%

The above table 1b shows that here predominately alkenes are formed butalso a comparatively high proportion of methane. However, only a smallamount of alcohols, namely ethanol, is formed.

For further comparison, the conversion with a Fischer-Tropsch reactorand a catalyst was simulated, as described in the literature by SyedNaqvi, SRI Consulting, Menlo Park, Calif. 94025, in PEP Review, 2007-2,December 2007, on page 5 in the right-hand column of table 1. Thecomposition of the product mixture is reproduced in the following table1c.

TABLE 1c F-T Product CO Selectivity C₁ (Methane)  8% C₂-C₄ 30% C₅-C₁₁36% C₁₂-C₁₉ 16% C₁₉₊  5% Oxygenates  5% Total 100%  C₃-C₄ Alkenes 87%C₃-C₄ Paraffins 13% Total 100%  C₅-C₁₂ (Alkenes) 70% C₅-C₁₂ (Alkanes)13% C₅-C₁₂ (Aromatics)  5% C₅-C₁₂ (Oxygenates) 12% Total 100%  C₁₃-C₁₈(Alkenes) 60% C₁₃-C₁₈ (Alkanes) 15% C₁₃-C₁₈(Aromatics) 15% ₁₃-C₁₈(Oxygenates) 10% Total 100% 

The above table 1c shows that here a multitude of compounds areproduced, namely higher alkanes with up to 20 carbon atoms, higheralkenes, aromatic hydrocarbons, and alcohols with up to 19 carbon atoms.The proportion of methane was 8%. A total of 30% of compounds withC2-C4, 36% of compounds with C5-C11, 12% of compounds with C12-C19, 5%of compounds with more than 19 carbon atoms and 5% of oxygenates wereformed. The selectivity of the formation of CO₂ is not represented.

EXAMPLE 2

In this example, the distribution of the compounds of the productmixture which arose after the synthesis of higher alcohols in the threephases which are formed after the separation stage with the absorptionmedium (in this example dodecane) is clarified, a mixture beingseparated which arose after the conversion with a catalyst according toexample 1, table 1. The catalyst comprised grains of nongraphitic carbonwith cobalt nanoparticles dispersed therein. In the example according totable 2a, the assumed CO conversion was 50% while that in the exampleaccording to table 2b was 75%. The different CO conversions in theindividual examples are achieved through the catalytic conversion of thesynthesis gas in one or more reactors placed in series with addition ofhydrogen at intervals for adjustment of the H₂:CO ratio of H₂:CO=1:1.

Example No. 2a: Variation CO conversion Catalyst: (see above)Composition synthesis gas Absorption medium Molar flow Mole fractionMolar flow [kmol/h] [%] [kmol/h] H₂ 5000 35% — CO 5000 35% — N₂ 4280 30%— n-Dodecane — — 3528

TABLE 2a CO conversion: 50% Crude Gas Aqueous Org. mol gas 10 phasephase phase absorbed/mol mol/h 12 Liquid 28 14 Total dodecane H₂ 175100%   0% 0%  0% 100% 5.0E−02 CO 2501 99%   1% 0%  1% 100% 7.1E−01 CO₂245 93%   7% 0%  7% 100% 6.9E−02 CH₄ 447 97%   3% 0%  3% 100% 1.3E−01 N₂4280 99%   1% 0%  1% 100% 1.2E+00 MeOH 93 1%  99% 82%  18% 100% 2.6E−02EtOH 57 0% 100% 68%  32% 100% 1.6E−02 1-PrOH 9 0% 100% 43%  57% 100%2.6E−03 1-BuOH 114 0% 100% 18%  82% 100% 3.2E−02 H₂O 1737 1%  99% 98%  1% 100% 4.9E−01 Ethane 57 82%   18% 0% 18% 100% 1.6E−02 Propane 36 43%  57% 0% 57% 100% 1.0E−02 n-Butane 19 0% 100% 0% 100%  100% 5.3E−03n-Pentane 1 0% 100% 0% 100%  100% 3.4E−04 Ethene 76 89%   11% 0% 11%100% 2.1E−02 Propene 126 53%   47% 0% 46% 100% 3.6E−02 1-Butene 45 0%100% 0% 100%  100% 1.3E−02 1-Pentene 21 0% 100% 0% 100%  100% 6.0E−03n-Dodecane 3528 0% 100% 0% 100%  100% 1.0E+00

Example No. 2b: Variation CO conversion Catalyst: as in examples 2 and2a Composition synthesis gas Absorption medium Molar flow Mole fractionMolar flow [kmol/h] [%] [kmol/h] H₂ 5000 35% — CO 5000 35% — N₂ 4280 30%— n-Dodecane — — 3528

TABLE 2b CO conversion: 75% Crude Gas Aqueous Org. mol gas 10 phasephase phase absorbed/mol mol/h 12 Liquid 28 14 Total dodecane H₂ 88 99%  1% 0%  1% 100% 1.3E−04 CO 1251 99%   1% 0%  1% 100% 3.8E−03 CO₂ 36792%   8% 0%  8% 100% 8.7E−03 CH₄ 671 96%   4% 0%  4% 100% 7.3E−03 N₂4280 99%   1% 0%  1% 100% 7.9E−03 MeOH 139 0% 100% 86%  14% 100% 3.9E−02EtOH 86 0% 100% 73%  27% 100% 2.4E−02 1-PrOH 14 0% 100% 50%  50% 100%4.0E−03 1-BuOH 171 0% 100% 24%  76% 100% 4.9E−02 H₂O 2606 1%  99% 99%  0% 100% 7.3E−01 Ethane 86 80%   20% 0% 20% 100% 5.0E−03 Propane 54 36%  64% 0% 64% 100% 9.7E−03 n-Butane 28 0% 100% 0% 100%  100% 8.0E−03n-Pentane 2 0% 100% 0% 100%  100% 5.1E−04 Ethene 113 87%   13% 0% 13%100% 4.1E−03 Propene 189 48%   52% 0% 52% 100% 2.8E−02 1-Butene 67 0%100% 0% 100%  100% 1.9E−02 1-Pentene 32 0% 100% 0% 100%  100% 9.0E−03n-Dodecane 3528 0% 100% 0% 100%  100% 1.0E+00

EXAMPLE 3

In the following example, the proportion of inert gas in the feed gasstream of the synthesis gas, which was catalytically converted to higheralcohols, i.e. the nitrogen content, varied with 10%, 20% and 30%(examples 3a, 3b and 3c). In this connection, the result was that theproportion of the lower alkenes and alkanes absorbed in the stage of theabsorption of the product mixture in the high boiling point hydrocarbonof the organic liquid phase in each case decreases with increasingproportion of inert gas. This is valid for ethane, propane, ethene andpropene, while the higher alkanes and alkenes from C4 in each case pass100% into the organic liquid phase.

Example No. 3a: Variation proportion inert gas Catalyst: as in examples2, 2a and 2b Composition synthesis gas Absorption medium Molar flow Molefraction Molar flow [kmol/h] [%] [kmol/h] H₂ 5000 45% — CO 5000 45% — N₂1110 10% — n-Dodecane — — 3528

TABLE 3a CO conversion: 50% Crude Gas Aqueous Org. mol gas 10 phaseLiquid phase phase absorbed/mol mol/h 12 phase 28 14 Total dodecane H₂175 99%   1% 0%  1% 100% 3.6E−04 CO 2501 98%   2% 0%  2% 100% 1.1E−02CO₂ 245 88%   12% 0% 12% 100% 8.5E−03 CH₄ 447 94%   6% 0%  6% 100%7.1E−03 N₂ 1110 99%   1% 0%  1% 100% 3.0E−03 MeOH 93 0% 100% 82%  18%100% 2.6E−02 EtOH 57 0% 100% 66%  34% 100% 1.6E−02 1-PrOH 9 0% 100% 42% 58% 100% 2.6E−03 1-BuOH 114 0% 100% 18%  82% 100% 3.2E−02 H₂O 1737 1% 99% 99%   1% 100% 4.9E−01 Ethane 57 70%   30% 0% 30% 100% 4.9E−03Propane 36 8%  92% 0% 92% 100% 9.4E−03 n-Butane 19 0% 100% 0% 100%  100%5.3E−03 n-Pentane 1 0% 100% 0% 100%  100% 3.4E−04 Ethene 76 81%   19% 0%19% 100% 4.0E−03 Propene 126 19%   81% 0% 81% 100% 2.9E−02 1-Butene 450% 100% 0% 100%  100% 1.3E−02 1-Pentene 21 0% 100% 0% 100%  100% 6.0E−03n-Dodecane 3528 0% 100% 0% 100%  100% 1.0E+00

Example No. 3b: Variation proportion inert gas Catalyst: as in example3a Composition synthesis gas Absorption medium Molar flow Mole fractionMolar flow [kmol/h] [%] [kmol/h] H₂ 5000 40% — CO 5000 40% — N₂ 2500 20%— n-Dodecane — — 3528

TABLE 3b CO conversion: 50% Crude Gas Aqueous Org. mol gas 10 phaseLiquid phase phase absorbed/mol mol/h 12 phase 28 14 Total dodecane H₂175 99%   1% 0%  1% 100% 2.7E−04 CO 2501 99%   1% 0%  1% 100% 8.2E−03CO₂ 245 91%   9% 0%  9% 100% 6.3E−03 CH₄ 447 96%   4% 0%  4% 100%5.3E−03 N₂ 2500 99%   1% 0%  1% 100% 5.3E−03 MeOH 93 0% 100% 82%  18%100% 2.6E−02 EtOH 57 0% 100% 67%  33% 100% 1.6E−02 1-PrOH 9 0% 100% 43% 57% 100% 2.6E−03 1-BuOH 114 0% 100% 18%  82% 100% 3.2E−02 H₂O 1737 1% 99% 99%   1% 100% 4.9E−01 Ethane 57 77%   23% 0% 23% 100% 3.8E−03Propane 36 25%   75% 0% 75% 100% 7.7E−03 n-Butane 19 0% 100% 0% 100% 100% 5.3E−03 n-Pentane 1 0% 100% 0% 100%  100% 3.4E−04 Ethene 76 86%  14% 0% 14% 100% 3.0E−03 Propene 126 38%   62% 0% 62% 100% 2.2E−021-Butene 45 0% 100% 0% 100%  100% 1.3E−02 1-Pentene 21 0% 100% 0% 100% 100% 6.0E−03 n-Dodecane 3528 0% 100% 0% 100%  100% 1.0E+00

Example No. 3c: Variation proportion inert gas Catalyst: as in examples3a and 3b Composition synthesis gas Absorption medium Molar flow Molefraction Molar flow [kmol/h] [%] [kmol/h] H₂ 5000 35% — CO 5000 35% — N₂4280 30% — n-Dodecane — — 3528

TABLE 3c CO conversion: 50% Crude Gas Aqueous Org. mol gas 10 phaseLiquid phase phase absorbed/mol mol/h 12 phase 28 14 Total dodecane H₂175 100%   0% 0%  0% 100% 5.0E−02 CO 2501 99%   1% 0%  1% 100% 7.1E−01CO₂ 245 93%   7% 0%  7% 100% 6.9E−02 CH₄ 447 97%   3% 0%  3% 100%1.3E−01 N₂ 4280 99%   1% 0%  1% 100% 1.2E+00 MeOH 93 1%  99% 82%  18%100% 2.6E−02 EtOH 57 0% 100% 68%  32% 100% 1.6E−02 1-PrOH 9 0% 100% 43% 57% 100% 2.6E−03 1-BuOH 114 0% 100% 18%  82% 100% 3.2E−02 H₂O 1737 1% 99% 98%   1% 100% 4.9E−01 Ethane 57 82%   18% 0% 18% 100% 1.6E−02Propane 36 43%   57% 0% 57% 100% 1.0E−02 n-Butane 19 0% 100% 0% 100% 100% 5.3E−03 n-Pentane 1 0% 100% 0% 100%  100% 3.4E−04 Ethene 76 89%  11% 0% 11% 100% 2.1E−02 Propene 126 53%   47% 0% 46% 100% 3.6E−021-Butene 45 0% 100% 0% 100%  100% 1.3E−02 1-Pentene 21 0% 100% 0% 100% 100% 6.0E−03 n-Dodecane 3528 0% 100% 0% 100%  100% 1.0E+00

EXAMPLE 4

In the following exemplary embodiment, the amount of substance of theabsorption medium used (in this instance dodecane) was varied each time.A product gas mixture which was obtained in the catalytic conversion ofa synthesis gas mixture with the composition given in example 1according to table 1 was subjected to the separation stage. In thisconnection, in four different simulations, 25%, 50%, 100% or 150% of theabsorption medium was used. The results are reproduced in the followingtables of examples 4a to 4d.

Example No. 4a: Variation absorption medium amount Catalyst: as inexample 3 Composition synthesis gas Absorption medium Molar flow Molefraction Molar flow [kmol/h] [%] [kmol/h] H₂ 5000 35% — CO 5000 35% — N₂4280 30% — n-Dodecane — — 886 (25%)

TABLE 4a CO conversion: 50% Crude Gas Aqueous Org. mol gas 10 phaseLiquid phase phase absorbed/mol mol/h 12 phase 28 14 Total dodecane H₂175 100%   0% 0%  0% 100% 2.5E−04 CO 2501 100%   0% 0%  0% 100% 7.5E−03CO₂ 245 98%  2% 0%  2% 100% 5.1E−03 CH₄ 447 99%  1% 0%  1% 100% 4.4E−03N₂ 4280 100%   0% 0%  0% 100% 7.4E−03 MeOH 93 14% 86% 79%   7% 100%8.9E−02 EtOH 57 11% 89% 74%  15% 100% 5.7E−02 1-PrOH 9  1% 99% 64%  36%100% 1.0E−02 1-BuOH 114  0% 100%  40%  60% 100% 1.3E−01 H₂O 1737  2% 98%98%   0% 100% 1.9E+00 Ethane 57 96%  4% 0%  4% 100% 2.9E−03 Propane 3688% 12% 0% 12% 100% 5.0E−03 n-Butane 19 63% 37% 0% 37% 100% 7.9E−03n-Pentane 1  3% 97% 0% 97% 100% 1.3E−03 Ethene 76 97%  3% 0%  3% 100%2.4E−03 Propene 126 90% 10% 0% 10% 100% 1.4E−02 1-Butene 45 68% 32% 0%32% 100% 1.6E−02 1-Pentene 21  9% 91% 0% 91% 100% 2.2E−02 n-Dodecane 886 0% 100%  0% 100%  100% 1.0E+00

Example No. 4b: Variation absorption medium amount Catalyst: as inexample 4a Composition synthesis gas Absorption medium Molar flow Molefraction Molar flow [kmol/h] [%] [kmol/h] H₂ 5000 35% — CO 5000 35% — N₂4280 30% — n-Dodecane — — 1767 (50%)

TABLE 4b CO conversion: 50% Crude Gas Aqueous Org. mol gas 10 phaseLiquid phase phase absorbed/mol mol/h 12 phase 28 14 Total dodecane H₂175 100%   0% 0%  0% 100% 2.3E−04 CO 2501 100%   0% 0%  0% 100% 6.8E−03CO₂ 245 97%  3% 0%  3% 100% 4.8E−03 CH₄ 447 98%  2% 0%  2% 100% 4.1E−03N₂ 4280 100%   0% 0%  0% 100% 7.1E−03 MeOH 93  7% 93% 82%  11% 100%4.9E−02 EtOH 57  1% 99% 76%  23% 100% 3.2E−02 1-PrOH 9  0% 100%  54% 46% 100% 5.3E−03 1-BuOH 114  0% 100%  28%  72% 100% 6.5E−02 H₂O 1737  1%99% 98%   0% 100% 9.7E−01 Ethane 57 91%  9% 0%  9% 100% 2.8E−03 Propane36 74% 26% 0% 26% 100% 5.3E−03 n-Butane 19 11% 89% 0% 89% 100% 9.5E−03n-Pentane 1  0% 100%  0% 100%  100% 6.8E−04 Ethene 76 95%  5% 0%  5%100% 2.3E−03 Propene 126 79% 21% 0% 21% 100% 1.5E−02 1-Butene 45 22% 78%0% 78% 100% 2.0E−02 1-Pentene 21  0% 100%  0% 100%  100% 1.2E−02n-Dodecane 1767  0% 100%  0% 100%  100% 1.0E+00

Example No. 4c: Variation absorption medium amount Catalyst: as inexamples 4a and 4b Composition synthesis gas Absorption medium Molarflow Mole fraction Molar flow [kmol/h] [%] [kmol/h] H₂ 5000 35% — CO5000 35% — N₂ 4280 30% — n-Dodecane — — 3528 (100%)

TABLE 4c CO conversion: 50% Crude Gas Aqueous Org. mol gas 12 phaseLiquid phase phase absorbed/mol mol/h 12 phase 28 14 Total dodecane H₂175 100%   0% 0%  0% 100% 5.0E−02 CO 2501 99%   1% 0%  1% 100% 7.1E−01CO₂ 245 93%   7% 0%  7% 100% 6.9E−02 CH₄ 447 97%   3% 0%  3% 100%1.3E−01 N₂ 4280 99%   1% 0%  1% 100% 1.2E+00 MeOH 93 1%  99% 82%  18%100% 2.6E−02 EtOH 57 0% 100% 68%  32% 100% 1.6E−02 1-PrOH 9 0% 100% 43% 57% 100% 2.6E−03 1-BuOH 114 0% 100% 18%  82% 100% 3.2E−02 H₂O 1737 1% 99% 98%   1% 100% 4.9E−01 Ethane 57 82%   18% 0% 18% 100% 1.6E−02Propane 36 43%   57% 0% 57% 100% 1.0E−02 n-Butan 19 0% 100% 0% 100% 100% 5.3E−03 n-Pentane 1 0% 100% 0% 100%  100% 3.4E−04 Ethene 76 89%  11% 0% 11% 100% 2.1E−02 Propene 126 53%   47% 0% 46% 100% 3.6E−021-Butene 45 0% 100% 0% 100%  100% 1.3E−02 1-Pentene 21 0% 100% 0% 100% 100% 6.0E−03 n-Dodecane 3528 0% 100% 0% 100%  100% 1.0E+00

Example No. 4d: Variation absorption medium amount Catalyst: as inexamples 4a to 4c Composition synthesis gas Absorption medium Molar flowMole fraction Molar flow [kmol/h] [%] [kmol/h] H₂ 5000 35% — CO 5000 35%— N₂ 4280 30% — n-Dodecane — — 5289 (150%)

TABLE 4d CO conversion: 50% Crude Gas Aqueous Org. mol gas 10 phaseLiquid phase phase absorbed/mol mol/h 12 phase 28 14 Total dodecane H₂175 99%   1% 0%  1% 100% 2.0E−04 CO 2501 99%   1% 0%  1% 100% 6.0E−03CO₂ 245 90%   10% 0% 10% 100% 4.7E−03 CH₄ 447 95%   5% 0%  5% 100%3.9E−03 N₂ 4280 99%   1% 0%  1% 100% 7.1E−03 MeOH 93 0% 100% 77%  23%100% 1.7E−02 EtOH 57 0% 100% 60%  40% 100% 1.1E−02 1-PrOH 9 0% 100% 35% 65% 100% 1.8E−03 1-BuOH 114 0% 100% 13%  87% 100% 2.2E−02 H₂O 1737 1% 99% 98%   1% 100% 3.3E−01 Ethane 57 73%   27% 0% 27% 100% 2.9E−03Propane 36 15%   85% 0% 85% 100% 5.8E−03 n-Butane 19 0% 100% 0% 100% 100% 3.5E−03 n-Pentane 1 0% 100% 0% 100%  100% 2.3E−04 Ethene 76 84%  16% 0% 16% 100% 2.3E−03 Propene 126 28%   72% 0% 72% 100% 1.7E−021-Butene 45 0% 100% 0% 100%  100% 8.5E−03 1-Pentene 21 0% 100% 0% 100% 100% 4.0E−03 n-Dodecane 5289 0% 100% 0% 100%  100% 1.0E+00

The amount of the absorption medium used (in the examples, dodecane wasused) was varied in the above examples 4a to 4d with 886 kmol/h, 1767kmol/h, 3528 kmol/h or 5289 kmol/h, it being possible to show that theamount of the alkenes and alkenes absorbed in the absorption mediumincreases approximately linearly with increasing molar flow, as expectedthe higher alkenes and alkanes (for example propene, propane) being morestrongly absorbed than the lower alkenes and alkanes (ethene, ethane).

The alcohols methanol, ethanol, propanol and butanol, in the absorptionoperation, pass partly into the aqueous phase and partly into thedodecane phase, methanol and ethanol, as expected, passing predominantlyinto the aqueous phase while butanol, even at a low molar flow, alreadypasses predominantly into the organic phase. The gases H₂, CO, CO₂, CH₄and N₂ remain in the gas phase in this separation stage. At a low molarflow of the absorption medium, though, the lower alkenes and alkanes andsometimes also amounts of the higher alkenes (propene, 1-butene) andalkanes (propane, butane) pass into the gas phase. This, however,changes with increasing molar flow of the absorption medium. Thus,already at a molar flow of 3528 kmol/h, about half of the propene and100% of the 1-butene passes into the organic liquid phase. At a stillhigher molar flow of 5289 kmol/h, the proportion of the propene absorbedin the organic phase increases even further. At a higher molar flow ofthe absorption medium, though, higher amounts of methanol and ethanoland also small amounts of CO₂ and CH₄ can also pass into the organicphase.

EXAMPLE 5

In the following exemplary embodiment, the catalyst was varied. Aproduct gas mixture which was obtained in the catalytic conversion of asynthesis gas mixture with the composition given in example 1 accordingto table 1b was subjected to the separation stage. For the simulation,the selectivity for CO₂ was determined from the difference from 100% byweight and the sum of all products. For the simulation of the separationprocess, the C₁₁₊ alkanes and the C₁₁₊ alkenes were assumed to beundecane or undecene.

Example No. 5: Variation catalyst Catalyst: Ru₃(CO)₁₂/CeO₂ (US 4 510 267A) Composition synthesis gas Absorption medium Molar flow Mole fractionMolar flow [kmol/h] [%] [kmol/h] H₂ 5000 35% — CO 5000 35% — N₂ 4280 30%— n-Dodecane — — 3528

TABLE 5 CO conversion: 75% Crude Gas Aqueous Org. mol gas 10 phaseLiquid phase phase absorbed/mol mol/h 12 phase 28 14 Total dodecane H₂<1 100%   0% 0%  0% 100% 2.3E−02 CO 1284 99%   1% 0%  1% 100% 7.9E+02CO₂ 141 92%   8% 0%  8% 100% 8.7E+01 CH₄ 444 97%   3% 0%  3% 100%2.7E+02 N₂ 4280 99%   1% 0%  1% 100% 2.6E+03 MeOH 0 0%  0% 0%  0%  0%0.0E+00 EtOH 30 0% 100% 75%   25% 100% 1.9E+01 H₂O 3404 0% 100% 99%   0%100% 2.1E+03 Ethane 17 80%   20% 0%  19% 100% 1.1E+01 Propane 18 34%  66% 0%  66% 100% 1.1E+01 n- Butane 15 0% 100% 0% 100% 100% 9.2E+00n-Pentane 9 0% 100% 0% 100% 100% 5.4E+00 n-Hexane 0 0%  0% 0%  0%  0%0.0E+00 n-Heptane 5 0% 100% 0% 100% 100% 2.8E+00 n-Octane 3 0% 100% 0%100% 100% 1.9E+00 n-Nonane 1 0% 100% 0% 100% 100% 8.3E−01 n-Decane 2 0%100% 0% 100% 100% 1.0E+00 n-Undecane 9 0% 100% 0% 100% 100% 5.5E+00Ethene 159 88%   12% 0%  12% 100% 9.8E+01 Propene 209 46%   54% 0%  54%100% 1.3E+02 1-Butene 123 0% 100% 0% 100% 100% 7.6E+01 1-Pentene 64 0%100% 0% 100% 100% 4.0E+01 1-Hexene 46 0% 100% 0% 100% 100% 2.8E+011-Heptene 24 0% 100% 0% 100% 100% 1.5E+01 1-Octene 12 0% 100% 0% 100%100% 7.6E+00 1-Nonene 8 0% 100% 0% 100% 100% 4.8E+00 1-Decene 5 0% 100%0% 100% 100% 3.3E+00 1-Undecene 24 0% 100% 0% 100% 100% 1.5E+01n-Dodecane 3528 0% 100% 0% 100% 100% 2.2E+03

The results of this exemplary embodiment show that even an olefin-richproduct gas mixture, which comprises a low proportion of alcohols, canbe subjected to the separation stage. With the exception of theshort-chain alkanes and alkenes (ethane, ethene, propane, propene), thealkanes and alkenes are virtually completely absorbed in the liquidphase and, after the phase separation, are virtually completely presentin the organic liquid phase.

LIST OF REFERENCE NUMERALS

10 feed inlet for the crude product gas stream

11 absorption apparatus

12 line for the discharge of the separated gaseous constituents

13 decanter

14 line for organic phase to the desorption apparatus

15 desorption apparatus

16 line for recycling the absorption medium

17 first distillation column

18 line for the feeding of the organic phase to the distillation column

19 line to the drying for alcohols separated in the distillation

20 line for hydrocarbons to the second distillation

21 second distillation column

22 line for the discharge of the hydrocarbons

23 return line for the recycling of the alcohols

24 third distillation column

25 molecular sieve

26 line for discharged water

27 product line for discharged alcohols

28 line for aqueous phase

29 line for alcohols

30 line for wastewater

1.-21. (canceled)
 22. A process for treating a gaseous material mixturethat has been obtained by catalytic conversion of synthesis gasrecovered from smelter gases, CO- or CO₂-rich gases, hydrogen, orbiomass, wherein the gaseous material mixture contains at least alkenesand alcohols, the process comprising: after the catalytic conversion ofthe synthesis gas, separating a product mixture obtained in thecatalytic conversion into a gas phase and a liquid phase by at leastpartial absorption of the alkenes in a high boiling point hydrocarbon orhydrocarbon mixture as an absorption medium; separating as the gas phasegases not absorbed into the absorption medium; and separating an aqueousphase from an organic phase of the absorption medium; desorption of thealkenes from the absorption medium, wherein the high boiling pointhydrocarbon or the hydrocarbon mixture used as the absorption mediumcomprises a diesel oil or an alkane with a viscosity of less than 10mPa·s at an ambient temperature and a boiling point of more than 200° C.23. The process of claim 22 comprising separating a mixture obtainedafter desorption comprising alkenes through a first distillation into afraction comprising predominantly the hydrocarbons and a fractioncomprising predominantly the alcohols.
 24. The process of claim 23comprising performing the first distillation at an elevated pressure ina pressure range from 10 bar to 40 bar.
 25. The process of claim 23comprising separating the hydrocarbons from the first distillation in asecond distillation that is an extractive distillation with water, fromresidues of alcohol and water present in the hydrocarbons.
 26. Theprocess of claim 22 comprising separating from water alcohols present inthe aqueous phase, after the separation of the aqueous phase from theorganic phase, in a third distillation by azeotropic distillation. 27.The process of claim 26 comprising separating a mixture obtained afterdesorption comprising alkenes through a first distillation into afraction comprising predominantly the hydrocarbons and a fractioncomprising predominantly the alcohols, wherein the alcohols separatedfrom the water in the third distillation are conveyed to the mixtureobtained after the desorption and, with this mixture, separated from thehydrocarbons through the first distillation.
 28. The process of claim 23comprising removing water from the fraction comprising predominantly thealcohols obtained in the first distillation by way of a molecular sieve.29. The process of claim 23 wherein an alcohol mixture obtained afterthe first distillation is subsequently separated through one or moredistillation stages into alcohol fractions with, each time, a differentnumber of carbon atoms, including a C1 fraction, a C2 fraction, a C3fraction, and a C4 fraction.
 30. The process of claim 25 wherein thealkenes present in the hydrocarbon mixture obtained after thedesorption, the alkenes present in the hydrocarbon mixture obtainedafter the first distillation, or the alkenes present in the hydrocarbonmixture obtained after the second distillation are converted byhydration to give alcohols.
 31. The process of claim 25 wherein thehydrocarbon mixture obtained after the second distillation is separatedinto fractions with, each time, the same number of carbon atoms,including a C3 fraction, a C4 fraction, and a C5 fraction.
 32. Theprocess of claim 23 wherein from the fraction comprising predominantlythe alcohols, lower alcohols methanol and ethanol and small amounts ofwater are separated in a column and a remaining alcohol mixture istreated with a higher hydrocarbon and is separated in a decanter into anorganic phase and an aqueous phase.
 33. The process of claim 32 whereinthe alcohols are stripped out from the organic phase in an additionalcolumn and residual water present in the alcohols is subsequentlyremoved using a molecular sieve.
 34. The process of claim 23 whereinfrom the fraction comprising predominantly the alcohols, lower alcoholsmethanol and ethanol are separated from higher alcohols in an extractivedistillation with ethylene glycol, wherein the higher alcohols aresubsequently separated from the ethylene glycol in an additionaldistillation column.
 35. The process of claim 23 wherein from thefraction comprising predominantly the alcohols, water is selectivelyremoved by pervaporation through a membrane and is withdrawn as permeatein vapor form.
 36. The process of claim 23 wherein from the fractioncomprising predominantly the alcohols, water is removed by azeotropicdistillation with a higher hydrocarbon.
 37. The process of claim 22wherein from the gaseous material mixture obtained after the catalyticconversion of synthesis gas, at least C4 alkenes and C5 alkenes arerecovered.
 38. The process of claim 37 wherein the desorption of thealkenes and the alcohols from the absorption medium is performed in adistillation column.
 39. The process of claim 38 wherein after thedesorption, the absorption medium is led back into a separation stage ofthe absorption.
 40. The process of claim 39 wherein the gas phaseseparated from the gases not absorbed in the absorption medium comprisesat least one of nitrogen, hydrogen, carbon monoxide, or carbon dioxide.41. The process of claim 22 wherein the gaseous material mixturecomprises nitrogen from blast furnace gas that is at least partlyremoved from a stream using a gas permeation membrane.